Seal configuration for electrochemical cell

ABSTRACT

An electrochemical cell includes a pair of bipolar plates and a membrane electrode assembly between the bipolar plates. The membrane electrode assembly comprises an anode compartment, a cathode compartment, and a proton exchange membrane disposed therebetween. The cell further includes a sealing surface formed in one of the pair of bipolar plates and a gasket located between the sealing surface and the proton exchange membrane. The gasket is configured to plastically deform to create a seal about one of the cathode compartment or the anode compartment. The sealing surface can include one or more protrusions.

This application claims the benefit of U.S. Provisional Application No.61/859,457, filed Jul. 29, 2013, which is incorporated herein byreference.

The present disclosure is directed towards an electrochemical cell, andmore specifically, to an electrochemical cell having a cascade sealingconfiguration and configured for hydrogen reclamation.

Electrochemical cells, usually classified as fuel cells or electrolysiscells, are devices used for generating current from chemical reactions,or inducing a chemical reaction using a flow of current. A fuel cellconverts the chemical energy of a fuel (e.g., hydrogen, natural gas,methanol, gasoline, etc.) and an oxidant (air or oxygen) intoelectricity and waste products of heat and water. A basic fuel cellcomprises a negatively charged anode, a positively charged cathode, andan ion-conducting material called an electrolyte.

Different fuel cell technologies utilize different electrolytematerials. A Proton Exchange Membrane (PEM) fuel cell, for example,utilizes a polymeric ion-conducting membrane as the electrolyte. In ahydrogen PEM fuel cell, hydrogen atoms can electrochemically split intoelectrons and protons (hydrogen ions) at the anode. The electrons flowthrough the circuit to the cathode and generate electricity, while theprotons diffuse through the electrolyte membrane to the cathode. At thecathode, hydrogen protons can react with electrons and oxygen (suppliedto the cathode) to produce water and heat.

An electrolysis cell represents a fuel cell operated in reverse. A basicelectrolysis cell can function as a hydrogen generator by decomposingwater into hydrogen and oxygen gases when an external electric potentialis applied. The basic technology of a hydrogen fuel cell or anelectrolysis cell can be applied to electrochemical hydrogenmanipulation, such as, electrochemical hydrogen compression,purification, or expansion.

An electrochemical hydrogen compressor (EHC), for example, can be usedto selectively transfer hydrogen from one side of a cell to another. AnEHC can comprise a proton exchange membrane sandwiched between a firstelectrode (i.e., an anode) and a second electrode (i.e., a cathode). Agas containing hydrogen can contact the first electrode and an electricpotential difference can be applied between the first and secondelectrodes. At the first electrode, the hydrogen molecules can beoxidized and the reaction can produce two electrons and two protons. Thetwo protons are electrochemically driven through the membrane to thesecond electrode of the cell, where they are rejoined by two reroutedelectrons and reduced to form a hydrogen molecule. The reactions takingplace at the first electrode and second electrode can be expressed aschemical equations, as shown below.First electrode oxidation reaction: H₂→2H⁺+2e ⁻Second electrode reduction reaction: 2H⁺+2e ⁻→H₂Overall electrochemical reaction: H₂→H₂

EHCs operating in this manner are sometimes referred to as a hydrogenpumps. When the hydrogen accumulated at the second electrode isrestricted to a confined space, the electrochemical cell compresses thehydrogen or raises the pressure. The maximum pressure or flow rate anindividual cell is capable of producing can be limited based on the celldesign.

To achieve greater compression or higher pressure, multiple cells can belinked in series to form a multi-stage EHC. In a multi-stage EHC the gasflow path, for example, can be configured so the compressed output gasof the first cell can be the input gas of the second cell.Alternatively, single-stage cells can be linked in parallel to increasethe throughput capacity (i.e., total gas flow rate) of an EHC. In both asingle-stage and multi-stage EHC, the cells can be stacked and each cellcan include a cathode, an electrolyte membrane, and an anode. Eachcathode/membrane/anode assembly constitutes a “membrane electrodeassembly”, or “MEA”, which is typically supported on both sides bybipolar plates. In addition to providing mechanical support, the bipolarplates physically separate individual cells in a stack whileelectrically connecting them. The bipolar plates also act as currentcollectors/conductors, and provide passages for the fuel. Typically,bipolar plates are made from metals, for example, stainless steel,titanium, etc., and from non-metallic electrical conductors, forexample, graphite.

Electrochemical hydrogen manipulation has emerged as a viablealternative to the mechanical systems traditionally used for hydrogenmanagement. Successful commercialization of hydrogen as an energycarrier and the long-term sustainability of a “hydrogen economy” dependslargely on the efficiency and cost-effectiveness of fuel cells,electrolysis cells, and other hydrogen manipulation/management systems(i.e., EHCs). Gaseous hydrogen is a convenient and common form forenergy storage, usually by pressurized containment. Advantageously,storing hydrogen at high pressure yields high energy density.

Mechanical compression is a traditional means to achieve compression.However, there are disadvantages to mechanical compression. For example,substantial energy usage, wear and tear on moving parts, excessivenoise, bulky equipment, and hydrogen embrittlement. Pressurization bythermal cycling is an alternative to mechanical compression, but likemechanical compression the energy usage is substantial. In contrast,electrochemical compression is quiet, scalable, modular, and can achievehigh energy efficiency.

One challenge for electrochemical hydrogen compression is the safetyconcern regarding pressurized hydrogen gas. Hydrogen gas is extremelyflammable and high pressure hydrogen gas raises safety issues. A majorconcern can include the leaking or unintended release of the highpressure gas from the electrochemical compressor. A catastrophic releasecould pose a safety hazard.

Moreover, even a small leak that may not rise to the level of asignificant safety concern, nonetheless reduces the efficiency of theelectrochemical compressor. Therefore, there is a need to prevent orreduce hydrogen leakage.

In consideration of the aforementioned circumstances, the presentdisclosure is directed toward an electrochemical cell having a sealconfiguration constructed to limit the unintended release of hydrogenfrom the cell. In addition, the seal configuration can enable thecollection and recycling of hydrogen leaked from the cell. In certainembodiments disclosed herein, a cascade seal configuration iscontemplated.

One aspect of the present disclosure is directed to an electrochemicalcell comprising: a pair of bipolar plates, wherein a sealing surface isformed in one of the pair of bipolar plates, a membrane electrodeassembly located between the pair of bipolar plates, wherein themembrane electrode assembly comprises an anode, a cathode, and a protonexchange membrane disposed therebetween; a first seal defining a highpressure zone, wherein the first seal is located between the bipolarplates and configured to contain a first fluid within the high pressurezone; a second seal defining an intermediate pressure zone, wherein thesecond seal is located between the bipolar plates and configured tocontain a second fluid within the intermediate pressure zone; whereinthe first seal is formed by a gasket that is configured to plasticallydeform to create a seal about one of the cathode compartment or theanode compartment. In certain embodiments, the sealing surface comprisesone or more protrusions.

Yet another aspect of the present disclosure is directed to a method ofsealing a compartment of an electrochemical cell. The method comprisesassembling an electrochemical cell having a pair of bipolar plates andan anode compartment, a cathode compartment, and a proton exchangemembrane disposed between the pair of bipolar plates. The method furtherincludes sealing a gasket against the one of the bipolar plates bycompressing the gasket with sufficient force to plastically deform thegasket, and sealing the proton exchange membrane against the gasket.

A further aspect of the present disclosure is directed to anelectrochemical cell. The electrochemical cell includes a pair ofbipolar plates and a membrane electrode assembly located between thepair of bipolar plates. The membrane electrode assembly comprises ananode compartment, a cathode compartment, and a proton exchange membranedisposed therebetween. The cell further includes a sealing surfaceformed in one of the pair of bipolar plates and a gasket located betweenthe sealing surface and the proton exchange membrane. The gasket isconfigured to plastically deform to create a seal about one of thecathode compartment or the anode compartment.

Another aspect of the present disclosure is directed to anelectrochemical cell. The electrochemical cell includes a pair ofbipolar plates and a membrane electrode assembly located between thepair of bipolar plates. The membrane electrode assembly comprises ananode compartment, a cathode compartment, and a proton exchange membranedisposed therebetween. The electrochemical cell further comprises asealing surface formed in one of the pair of bipolar plates, and thesealing surface comprises one or more protrusions. A compressed gasketlocated between the sealing surface and the proton exchange membrane,and the gasket is plastically deformed to create a seal about one of thecathode compartment or the anode compartment.

Yet another aspect of the present disclosure is directed to anelectrochemical cell. The electrochemical cell includes a pair ofbipolar plates and a membrane electrode assembly located between thepair of bipolar plates. The membrane electrode assembly comprises ananode compartment, a cathode compartment, and a proton exchange membranedisposed therebetween. The electrochemical cell further comprises asealing surface formed in one of the pair of bipolar plates; and agasket located between the sealing surface and the proton exchangemembrane, wherein the gasket comprises at least one protrusion.

A further aspect of the present disclosure is directed to anelectrochemical cell. The electrochemical cell includes a pair ofbipolar plates and a membrane electrode assembly located between thepair of bipolar plates. The membrane electrode assembly comprises ananode compartment, a cathode compartment, and a proton exchange membranedisposed therebetween. The electrochemical cell further comprises asealing surface formed in one of the pair of bipolar plates; and acompressed gasket located between the sealing surface and the protonexchange membrane. The gasket comprises at least one protrusion prior tocompression.

An additional aspect of the present disclosure is directed to anelectrochemical cell comprising: a pair of bipolar plates and a membraneelectrode assembly located between the pair of bipolar plates, whereinthe membrane electrode assembly comprises an anode, a cathode, and aproton exchange membrane disposed therebetween; a first seal defining ahigh pressure zone, wherein the first seal is located between thebipolar plates and configured to contain a first fluid within the highpressure zone; a second seal defining an intermediate pressure zone,wherein the second seal is located between the bipolar plates andconfigured to contain a second fluid within the intermediate pressurezone; and wherein the first seal is configured to leak the first fluidinto the intermediate pressure zone when the first seal unseats.

Another aspect of the present disclosure is directed to anelectrochemical cell comprising: a pair of bipolar plates and a membraneelectrode assembly located between the pair of bipolar plates; a highpressure zone located between the bipolar plates containing a firstfluid; an intermediate pressure zone located between the bipolar platescontaining a second fluid; and a low pressure zone containing a thirdfluid; wherein the electrochemical cell is configured to transitionbetween a first configuration, a second configuration, and a thirdconfiguration based on at least one of a closing force applied to thebipolar plates and an opening force produced by a pressure of at leastone of the first fluid, second fluid, and third fluid.

Yet another aspect of the present disclosure is directed to a method oftuning the closing force of an electrochemical cell having a cascadeseal configuration, the method comprising: providing an electrochemicalcell having a plurality of seals in a cascade seal configuration;applying an initial closing force to the electrochemical cell based onthe expected operating pressure; operating the electrochemical cell;monitoring the pressure of the electrochemical cell; and adjusting theclosing force applied to the electrochemical cell based on the monitoredpressure, wherein adjusting the closing force changes the pressure atwhich at least one of the plurality of seals unseats.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a side view of part of an electrochemical cell, showingvarious components of an electrochemical cell.

FIG. 2A is a front view of part of an electrochemical cell, showing thevarious seals and pressure zones of the cell, according to an exemplaryembodiment.

FIG. 2B is a front view of part of an electrochemical cell, showing thevarious seals and pressure zones of the cell, according to an exemplaryembodiment.

FIG. 3A is a cross-sectional view of part of an electrochemical cell,according to an exemplary embodiment.

FIG. 3B is a cross-sectional view of part of an electrochemical cell,showing various forces, according to an exemplary embodiment.

FIG. 4A is a cross-sectional view of part of an electrochemical cell,showing a first configuration, according to an exemplary embodiment.

FIG. 4B is a cross-sectional view of part of an electrochemical cell,showing a second configuration, according to an exemplary embodiment.

FIG. 4C is a cross-sectional view of part of an electrochemical cell,showing a third configuration, according an exemplary embodiment.

FIG. 5 is schematic diagram showing an electrochemical hydrogenreclamation system, according to an exemplary embodiment.

FIG. 6 is a flow diagram illustrating a method of controlling thepressure within an electrochemical cell, according to an exemplaryembodiment.

FIG. 7 is a front view of part of an electrochemical cell, showing thevarious seals and pressure zones of the cell, according to anotherembodiment.

FIG. 8 is a cross-sectional view of a part of an electrochemical cell,showing a sealed cathode compartment, according to an exemplaryembodiment.

FIGS. 9A-9C are cross-sectional views showing a sealing surface of abipolar plate including protrusions having various configurations,according to exemplary embodiments.

FIGS. 9D and 9E are cross-sectional views of the sealing surface of abipolar plate depicted in FIG. 9A, in an uncompressed and compressedstate, respectively.

FIG. 9F is a cross-sectional view of the sealing surface of a bipolarplate depicted in FIG. 9A containing dimensional information.

FIG. 10 is a cross-sectional view of a gasket having protrusions,according to an exemplary embodiment.

FIG. 11 is a top cross-sectional view of a part of an electrochemicalcell, showing a sealed cathode compartment, according to anotherembodiment.

FIG. 12A is a top cross-sectional view of a part of an electrochemicalcell, showing a gas diffusion layer and a reinforcement layer betweenthe anode compartment and the PEM, according to an exemplary embodiment.

FIG. 12B is a top cross-sectional view of a part of an electrochemicalcell, showing a reinforcement layer having a portion extending beyondthe length of the gasket, according to another exemplary embodiment.

FIG. 12C is a top cross-sectional view of a part of an electrochemicalcell, showing a reinforcement layer between the gasket and the PEM,according to an exemplary embodiment.

FIG. 12D is a top cross-sectional view of a part of an electrochemicalcell, showing a reinforcement layer having a portion extending beyondthe length of the gasket, according to another exemplary embodiment.

FIG. 13 is a cross-sectional view of a part of an electrochemical cell,showing a shim for use during ex-situ testing of the electrochemicalcell, according to an exemplary embodiment.

FIG. 14 is an isometric view of a two-piece bipolar plate, according toan exemplary embodiment.

Reference will now be made in detail to the present exemplaryembodiments of the present disclosure, examples of which are illustratedin the accompanying drawings. Wherever possible, the same referencenumbers will be used throughout the drawings to refer to the same orlike parts. Although described in relation to an electrochemical cellemploying hydrogen, it is understood that the devices and methods of thepresent disclosure can be employed with various types of fuel cells andelectrochemical cells, including, but not limited to electrolysis cells,hydrogen purifiers, hydrogen expanders, and hydrogen compressors.

FIG. 1 shows an exploded side view of an electrochemical cell 100,according to an exemplary embodiment. Electrochemical cell 100 cancomprise an anode 110, a cathode 120, and a proton exchange membrane(PEM) 130 disposed in between anode 110 and cathode 120. Anode 110,cathode 120, and PEM 130 combined can comprise a membrane electrodeassembly (MEA) 140. PEM 130 can comprise a pure polymer membrane orcomposite membrane where other material, for example, silica,heteropolyacids, layered metal phosphates, phosphates, and zirconiumphosphates can be embedded in a polymer matrix. PEM 130 can be permeableto protons while not conducting electrons. Anode 110 and cathode 120 cancomprise porous carbon electrodes containing a catalyst layer. Thecatalyst material, for example platinum, can increase the reaction rate.

Electrochemical cell 100 can further comprise two bipolar plates 150,160. Bipolar plates 150, 160 can act as support plates, conductors,provide passages to the respective electrode surfaces for the fuel, andprovide passages for the removal of the compressed fuel. Bipolar plates150, 160 can also include access channels for cooling fluid (i.e.,water, glycol, or water glycol mixture). The bipolar plates can be madefrom aluminum, steel, stainless steel, titanium, copper, Ni—Cr alloy,graphite or any other electrically conductive material or combination ofthese materials in the form of alloys, coatings or claddings. Bipolarplates 150, 160 can separate electrochemical cell 100 from theneighboring cells in an electrochemical stack (not shown). For example,multiple electrochemical cells 100 can be linked in fluidic series toform a multi-stage electrochemical hydrogen compressor (EHC) or stackedin fluidic parallel to form a single-stage EHC.

In operation, according to an exemplary embodiment, hydrogen gas can besupplied to anode 110 through bipolar plate 150. An electric potentialcan be applied between anode 110 and cathode 120, wherein the potentialat anode 110 is greater than the potential at cathode 120. The hydrogenat anode 110 can be oxidized causing the hydrogen to split intoelectrons and protons. The protons are electrochemically transported or“pumped” through PEM 130 while the electrons are rerouted around PEM130. At cathode 120 on the opposite side of PEM 130 the transportedprotons and rerouted electrons are reduced to form hydrogen. As more andmore hydrogen is formed at cathode 120, the hydrogen can be compressedand pressurized within a confined space.

Within electrochemical cell 100, a plurality of different pressure zonesand a plurality of seals can define one or more different pressurezones. FIG. 2A shows the plurality of different seals and pressure zoneswithin electrochemical cell 100. As shown in FIG. 2A, the plurality ofseals can include a first seal 171, a second seal 181, and a third seal191. First seal 171 can be contained entirely within second seal 181 andsecond seal 181 can be contained entirely within third seal 191. Inaddition, the plurality of seals can further include ancillary firstseals 175, 176. Ancillary seal 175 and 176 can be located outside firstseal 171, but within second seal 181.

First seal 171 can define high pressure zone 170 and be configured tocontain a first fluid 172 (e.g., hydrogen) within high pressure zone170. First seal 171 can delimit the outer boundaries of high pressurezone 170. High pressure zone 170 can correspond to the high pressurecathode 120 side of PEM 130. Hydrogen formed at cathode 130 can becollected in high pressure zone 170 and contained by first seal 171.Hydrogen within high pressure zone 170 can be compressed and, as aresult, increase in pressure as more and more hydrogen is formed in highpressure zone 170. Hydrogen in high pressure zone 170 can be compressedto a pressure up to or greater than 15,000 psig.

Ancillary first seals 175, 176 can define two ancillary high pressurezones 177, 178 that can be in fluid communication with high pressurezone 170. Ancillary high pressure zones 177, 178 can be common passagesconfigured to discharge the first fluid 172 from high pressure zone 170.Ancillary high pressure zones 177, 178 can be in fluid communicationwith common passages of adjacent electrochemical cells in a multi-cellelectrochemical compressor.

Second seal 181 can define intermediate pressure zone 180 and beconfigured to contain a second fluid 182 within intermediate pressurezone 180. Second seal 181 can delimit the outer boundaries ofintermediate pressure zone 180. Intermediate pressure zone 180 cancorrespond to the low pressure anode 110 side of PEM 130. Second fluid182 (e.g., hydrogen or gas mixture containing hydrogen) supplied toanode 110 can be contained in intermediate pressure zone 180 by secondseal 181 until it is oxidized and “pumped” across PEM 130 to cathode 120and high pressure zone 170. Second fluid 182 within intermediatepressure zone 180 can vary based on the pressure being supplied.Regardless, second fluid 182 in intermediate pressure zone 180 cangenerally be lower pressure than first fluid 172 in high pressure zone170.

Third seal 191 can define low pressure zone 190 and be configured tocontain a third fluid 192 within low pressure zone 190. Third seal 191can delimit the outer boundaries of low pressure zone 190. Low pressurezone 190 can comprise coolant fluid passages and third fluid 192 cancomprise coolant fluid. Coolant fluid can include water, glycol, orcombination thereof. In a high temperature system oil can be used as acoolant fluid. Third fluid 192 can generally be maintained at a pressureless than the pressure of second fluid 182 in intermediate pressure zone180 and first fluid 172 in high pressure zone 170. Low pressure zone 190can include an inlet passage and outlet passage (not shown) configuredso third fluid 192 can be circulated through low pressure zone 190.

In an alternate embodiment as shown in FIG. 2B, low pressure zone 190can be located not within electrochemical cell 100, but rather in thearea surrounding electrochemical cell 100 or a plurality of cellsforming a stack. For example, low pressure zone 190 can contain nitrogen192 forming a nitrogen blanket surrounding electrochemical cell 100 orin other embodiments surrounding a stack of cells. Other inert fluidssuch as argon or helium could also be used in place of nitrogen.

FIG. 3A shows a cross-sectional view of electrochemical cell 100 alongplane A of FIG. 2A. As described in FIG. 2A, electrochemical cell 100can comprise MEA 140 and bipolar plates 150, 160. Between bipolar plates150, 160 can be first seal 171 defining high pressure zone 170, secondseal 181 defining intermediate pressure zone 180, and third seal 191defining low pressure zone 190. In FIG. 3A, first seal 171, second seal181, and third seal 191 can each be shown as two separate cross-sectionsof a single continuous seal as previously shown in FIG. 2A.

As shown in FIG. 3A, first seal 171 can be positioned against a firstshoulder 173. First shoulder 173 can be configured to maintain theposition of first seal 171 as pressure can build within high pressurezone 170. Pressure within high pressure zone 170 can apply an outwardforce against first seal 171. The height of first shoulder 173 can rangefrom about 98% to about 25% of the uncompressed thickness of first seal171.

In the particular embodiment shown in FIG. 3A there is no shoulderlocated interior to first seal 171. The absence of an interior shoulderas shown in FIG. 3A can allow for first seal 171 to be combined, joined,connected, or integral to MEA 140 or portion thereof. Having first seal171 integral to MEA 140 can facilitate consistent, efficient, andstreamlined assembly of electrochemical cell 100. However, in alternateembodiments an additional shoulder can be positioned interior to firstseal 171 that can be configured to create a groove in which first seal171 can be positioned.

Referring again to FIG. 3A, second seal 181 can be positioned in asecond groove 183 formed between two shoulders in bipolar plate 160. Tothe interior of second groove 183 and second seal 181 can beintermediate pressure zone 180 and to the exterior of second groove 183and second seal 181 can be low pressure zone 190. The depth of secondgroove 183 can range from about 98% to about 25% of the uncompressedthickness of second seal 181.

Third seal 191 as shown in FIG. 3A, can be positioned in a third groove193 formed between two shoulders in bipolar plate 160. To the interiorof third groove 193 and third seal 191 can be low pressure zone 190 andto the exterior third groove 193 and third seal 191 can be thesurrounding environment of electrochemical cell 100. The depth of thirdgroove 193 can range from about 98% to about 25% of the uncompressedthickness of third seal 191.

During assembly first seal 171, second seal 181, and third seal 191between bipolar plate 150, 160 can be compressed by a predeterminedpercentage of their uncompressed thickness by selecting the appropriateheight of their respective shoulders 173 or depth of their respectivegrooves, 183 and 193. First shoulder 173 and the shoulders formingsecond groove 183 and third groove 193 can act as a stop, as shown inFIG. 3A, for bipolar plate 150. By acting as a stop the possibility ofover compressing the seals can be reduced. The elevation of firstshoulder 173 and the shoulders forming second groove 183 and thirdgroove 193 can be equal, such that, bipolar plate 150 can make contactwith all the shoulder surfaces of bipolar plate 160 at once when thesurfaces are parallel.

In alternate embodiments (not shown), second groove 183 and third groove193 can be formed in bipolar plate 150 rather than bipolar plate 160. Inanother embodiment, second groove 183 can be formed in either bipolarplate 150, 160 while third groove 193 is formed in the other plate. Inyet another embodiment, portions of second groove 183 and third groove193 can be formed in both bipolar plates 150, 160.

Second groove 183 and third groove 193 can have a cross-sectionalgeometry that corresponds to the shape of second seal 181 and third seal191. For example, the geometry of the seal and groove cross-section canbe a square, rectangle, triangle, polygon, circle, or oval. In variousembodiments the width of second seal 181 and third seal 191 can be lessthan the corresponding groove. The additional space in the grooves canallow for the expanding and contracting of the seals caused bytemperature change, pressure change from the internal gases, andpressure change from the bipolar plate compression. As shown in FIG. 3A,typically the seals can be forced outwardly to the outer most positionwithin the grooves because the seals experience higher pressure from theinterior side versus the exterior side.

First seal 171, second seal 181, and third seal 191 can be a gasket,o-ring, or other sealing component. First seal 171, second seal 181, andthird seal 191 can be made of an elastomeric or polymeric sealingmaterial, for example, silicone, EPDM (ethylenepropylene-diene-monomer),fluoroelastomer, nitrile rubber (Buna-N), PTFE(polytetrafluoroethylene), polysulfone, polyetherimide, polyphenylenesulfide, PEEK (polyether ether ketone), polyimide, PET (polyethyleneterephthalate), PEN (polyethylene naphthalate), HDPE (high-densitypolyethylene), polyurethane, neoprene, acetal, nylon, polybutyleneterephthalate, NBR (acrylonitrile-butadiene rubber), etc. In someembodiments, first seal 171, second seal 181, and third seal 191 can bemade from metal material including, for example, tin, tin alloys,stainless steel, silver, platinum, and gold. The material of each sealcan be different than the material of the other seals, the material canbe the same for just two of the seals, or the material can be the samefor all the seals.

Like the material, the thickness of each seal can be different than theother seals. Thickness can be measured along a vertical axis (Y) ofelectrochemical cell 100. As shown in FIG. 3A, the thickness of secondseal 181 is greater than the thickness of first seal 171 and thethickness of third seal 191 is greater than the thickness of second seal181. Consequently, the outermost seal, third seal 191, can have thegreatest thickness and the innermost seal, first seal 171, can have thesmallest thickness. For example, the thickness of first seal 171 canrange between about 0.01 mm and about 1.0 mm, the thickness of secondseal 181 can range between about 0.02 mm and about 2.0 mm, and thethickness of third seal 191 can range between about 0.03 mm and 3.0 mm.

For embodiments where the cross-sectional geometry of first seal 171,second seal 181, and third seal 191 can be a circle or oval, thethickness as described above can refer to the diameter of the circle oroval cross-section.

As shown in FIG. 3B, during operation of electrochemical cell 100, thepressure of first fluid 172, second fluid 182, and third fluid 192applied within each corresponding zone between bipolar plates 150, 160can produce an opening force 200. Opening force 200 unopposed can causebipolar plate 150, 160 to separate. In order to prevent opening force200 from separating bipolar plates 150, 160, a closing force 210 can beapplied to the plates to oppose and overcome opening force 200. It isunderstood that the pressure of first fluid 172, second fluid 182, andthird fluid 192 would produce more forces than those represented by theplurality of arrows representing opening force 200. For example, lateralforces (not shown) perpendicular to opening force 200 would be producedas well as other forces pointing outwardly from each pressure zone inall possible directions.

FIG. 4A shows a cross-section of electrochemical cell 100 in a firstconfiguration. Electrochemical cell 100 can maintain first configurationwhen closing force 210 is sufficient to overcome opening force 200 andhold bipolar plates 150, 160 substantially together. While in firstconfiguration first seal 171, second seal 181, and third seal 191 canall maintain contact with both the top and bottom sealing surfaces ofbipolar plate 150, 160, preventing leaking or bypassing of first fluid172, second fluid 182, or third fluid 192. In this particular situation,all seals are fulfilling their function.

When electrochemical cell 100 is in first configuration, as describedabove, the actual measurement of the separation between the surfaces ofbipolar plates 150, 160 can vary. For example, the separation can rangefrom about 0.00 mm to about 0.01 mm, to about 0.05 mm, to about 0.10 mm.

FIG. 4B shows a cross-section of electrochemical cell 100 in a secondconfiguration. Electrochemical cell 100 can change to secondconfiguration when closing force 210 is reduced or opening force 200 isincreased (e.g., first fluid 172 pressure increases) causing bipolarplates 150, 160 to separate. As shown in FIG. 4B, the first separationof bipolar plates 150, 160 can cause first seal 171 to unseat allowingthe bypass of first fluid 172 from high pressure zone 170 intointermediate pressure zone 180. In the particular embodiment shown inFIG. 4B, first seal 171 is shown to unseat from bipolar plate 160 first,allowing the flow of first fluid 172 under and around first seal 171.However, it is understood that in alternate embodiments (not shown),first seal 171 can unseat from bipolar plate 150 first, allowing theflow of first fluid 172 over first seal 171 by passing between firstseal 171 and MEA 140.

The flow of first fluid 172 from high pressure zone 170 to intermediatepressure zone 180 can be caused by the pressure differential betweenfirst fluid 172 and second fluid 182 and may travel along the path ofleast resistance. First seal 171 can be configured to be the first ofthe seals to unseat by having a thickness less than second seal 181 andthird seal 191. This can allow third seal 191 and second seal 181 tomaintain contact with both sealing surfaces preventing fluid frombypassing either seal despite the first separation of bipolar plates150, 160 present in second configuration.

When electrochemical cell 100 is in second configuration, as describedabove, the actual measurement of the first separation that existsbetween bipolar plates 150, 160 can vary. For example, first separationcan range from about 0.01 mm to about 0.05 mm, to about 0.10 mm, toabout 0.25 mm.

FIG. 4C shows a cross-section of electrochemical cell 100 in a thirdconfiguration. Electrochemical cell 100 can change to thirdconfiguration when closing force 210 is further reduced or opening force200 is further increased causing bipolar plates 150, 160 to undergosecond separation. As shown in FIG. 4C, second separation of bipolarplates 150, 160 can cause both first seal 171 and second seal 181 tounseat allowing the bypass of first fluid 172 from high pressure zone170 and second fluid 182 from intermediate pressure zone 180 into lowpressure zone 190. In the particular embodiment shown in FIG. 4C, secondseal 181 is shown to unseat from bipolar plate 150 first, allowing theflow of second fluid 182 over second seal 181. However, it is understoodthat in alternate embodiments (not shown), second seal 181 can unseatfrom bipolar plate 160 first, allowing the flow of second fluid 182under and around second seal 181.

The flow of second fluid 182 from intermediate pressure zone 180 to lowpressure zone 190 can be caused by the pressure differential betweensecond fluid 182 and third fluid 192. Second seal 181 can be configuredto be the second seal to unseat by being thicker than first seal 171,but not as thick as third seal 191. Therefore, because third seal 191can be thicker than both first seal 171 and second seal 181, third seal191 can maintain contact with both sealing surfaces preventing flow frombypassing notwithstanding the second separation of bipolar plates 150,160.

When electrochemical cell 100 is in third configuration, as describedabove, the actual measurement of the second separation can vary. Forexample, second separation can range from about 0.05 mm to about 0.25mm, to about 0.50 mm.

Electrochemical cell 100 can be configured to transition from firstconfiguration to second configuration and second configuration to thirdconfiguration based on the changing magnitude of closing force 210 andopening force 200 during operation. In addition, electrochemical cell100 can also transition from third configuration to second configurationand second configuration to first configuration based on the changingmagnitude of closing force 210 and opening force 200. It is contemplatedthat transitioning between first configuration, second configuration,and third configuration can occur continuously during the operation inresponse to the changing magnitude of closing force 210 and openingforce 200.

In other embodiments, it is contemplated that the modulus of elasticityor durometer of the seals can be different instead of the thickness ofthe seals to enable the dispersed unseating of the seals. In yet anotherembodiment, both the thickness and the modulus of elasticity can bevaried.

In certain embodiments, arrangement of the seals as described above canbe classified as a cascade seal configuration. The cascade sealconfiguration can provide several advantages. For example, the cascadeseal configuration can limit the potential of high pressure hydrogenescaping electrochemical cell 100 by providing seal redundancy in theform of three levels of sealing protection. Reducing the potential ofhydrogen leaks can benefit safety and energy efficiency.

In addition, the cascade seal configuration can also allow forself-regulation of pressure. Self-regulation of pressure can be achievedbecause of the disparity in seal thickness and the resulting dispersedunseating of first seal 171, second seal 181, and third seal 191. Forexample, when electrochemical cell 100 is in second configuration asshown in FIG. 4B, first seal 171 can unseat allowing first fluid 172 toleak into intermediate pressure zone 180. First fluid 172 leaking intointermediate pressure zone 180 can bleed pressure from high pressurezone 170. By bleeding pressure from high pressure zone 170, openingforce 200 can be reduced. The drop in opening force 200 can allow thefirst separation of bipolar plates 150, 160 to be reversed causing thetransition of electrochemical cell 100 from second configuration tofirst configuration and the reseating of first seal 171.

First fluid 172 that leaks by first seal 171 can combine with secondfluid 182 and be utilized by electrochemical cell 100, in effect, theleaked first fluid 172 can be recycled. A consequence of this leakingand subsequent recycling can be a loss in compression efficiency becausethe leaked hydrogen is “pumped” through PEM 130 twice. However, thepotential loss in compression efficiency is still less than the overallloss in efficiency would be if the leaked hydrogen was not recovered aninstead leaked to the exterior of electrochemical cell 100 and was lost.

In the event the bleeding of pressure from high pressure zone 170 is notenough to cause the transition from second configuration to firstconfiguration, second separation may occur causing electrochemical cellto transition from second configuration to third configuration. In thirdconfiguration as shown in FIG. 4C, the second separation of bipolarplates 150, 160 can cause second seal 181 to unseat allowing secondfluid 182 to leak into low pressure zone 190. Second fluid 182 leakinginto low pressure zone 190 can bleed pressure from intermediate pressurezone 180. By bleeding pressure from intermediate pressure zone 180,opening force 200 can be further reduced. The drop in opening force 200can allow the second separation of bipolar plates 150, 160 to bereversed causing the transition of electrochemical cell 100 from thirdconfiguration to second configuration and the reseating of at leastsecond seal 181.

The consequence of bleeding second fluid 182 from intermediate pressurezone 180 to low pressure zone 190 can be a loss of cell efficiency.However, a benefit can be reducing the possibility of second fluid 182(i.e., hydrogen gas) from escaping electrochemical cell 100.

In various embodiments, the pressure of third fluid 192 in low pressurezone 190 can be monitored. The unseating of second seal 181 can resultin a pressure increase in low pressure zone 190 caused by the bleedingof second fluid 182 pressure into low pressure zone 190. Therefore, bymonitoring the pressure of third fluid 192 the unseating of second seal181 can be detected. In addition, electrochemical cell 100 can beconfigured to shut down before the pressure in low pressure zone 190reaches a critical pressure. The critical pressure can be set just belowthe pressure at which third seal 191 would unseat allowing first fluid172, second fluid 182, and third fluid 192 to escape electrochemicalcell 100.

Monitoring the pressure can be accomplished in a variety of means. Forexample, a pressure transmitter could be configured to read the pressurein intermediate or low pressure zones 180 or 190, respectively, and whenthe pressure reaches the critical pressure set point the electricalpotential to anode 110 and cathode 120 could be turned off preventingfurther hydrogen from getting “pumped” across PEM 130.

In other embodiments, the pressure of second fluid 182 in intermediatepressure zone 180 and first fluid 172 in high pressure zone 170 can alsobe monitored. For example, monitoring the pressure of second fluid 182can allow the cell to be shut down before the pressure reaches the pointwhere second seal 181 could unseat.

In various embodiments, when first fluid 172 or second fluid 182 (e.g.,high or low pressure hydrogen) bleeds into low pressure zone 190 it cancombine with third fluid 192 (e.g., coolant fluid) and can be carriedout of low pressure zone 190 by the circulating third fluid 192.

FIG. 5 shows an electrochemical hydrogen reclamation system (EHRS) 500,according to an exemplary embodiment. EHRS 500 can comprise anelectrochemical cell 100 as described above having a cascade sealconfiguration. In addition to electrochemical cell 100, EHRS 500 cancomprise a hydrogen reclamation apparatus 510. Apparatus 510 can be influid communication with low pressure zone 190 and intermediate pressurezone 180 of electrochemical cell 100. Apparatus 510 can receive thirdfluid 192 discharged from low pressure zone 190 and can be configured torecover at least a portion of any second fluid 182 contained in thirdfluid 192. After third fluid 192 passes through hydrogen reclamationapparatus 510, third fluid can be resupplied to low pressure zone 190.Any second fluid 182 recovered from third fluid 192 by hydrogenreclamation apparatus 510 can be reintroduced into intermediate pressurezone 180 by way of a recycle line 520 configured to fluidly connecthydrogen reclamation apparatus 510 and intermediate pressure zone 180.Recycling second fluid 182 can improve overall system efficiency. Whensecond fluid 182 is hydrogen gas, for example, recycling second fluid182 reduces the amount of new hydrogen required.

Hydrogen reclamation apparatus 510 can use a variety of technologies toseparate second fluid 182 from third fluid 192. For example, dissolvedgas separation from liquid coolant or hydrogen separation membrane froma nitrogen blanket.

In various embodiments, EHRS 500 can be configured to monitor thepressure of third fluid 192 in low pressure zone 190. By monitoring thepressure of third fluid 192 in low pressure zone 190, hydrogenreclamation apparatus 510 can be configured to only be engaged orenergized when an increased pressure has been detected, which canindicate second seal 182 has unseated and second fluid has leaked intolow pressure zone 190. By limiting the use of hydrogen reclamationapparatus the overall system efficiency can be increased.

Electrochemical cell 100 can operate at differential pressures higherthan about 15,000 psig. For example, a differential pressure can bemeasured as the difference between second fluid 182 pressure (i.e., theinlet hydrogen pressure) which can range from about −10 psig to about 0psig, or from about 0 psig to about 25 psig, about 100 psig, about 500psig, about 1,000 psig, or about 6,000 psig and first fluid 172 pressure(i.e., compressed hydrogen pressure) which can range from the lowerbound of the inlet hydrogen pressure to higher than about 15,000 psig.The differential pressure as described above can be the differentialpressure experienced by first seal 171. Second seal 181 can experiencedifferential pressure between second fluid 182 and third fluid 192ranging between about 0 psig to about 25 psig, about 100 psig, about 500psig, about 1,000 psig, or about 6,000 psig.

The cascade seal configuration describe above can enable closing force210 to be tuned (i.e., increased or decreased) to a particular openingforce 200. Traditionally closing force 210 can be set to deliver apreload on first seal 171, second seal 181, and third seal 191sufficient to withstand the expected opening force 200 caused by theinternal pressure. However, by changing the preload or adjusting closingforce 210 during operation of electrochemical cell 100, the pressure atwhich first seal 171, second seal 181, and third seal 191 unseat can betuned so they each unseat and leak at a preferred particular pressure.

The tuning capability of electrochemical cell 100 can be used to enhancethe safety of the device. As described above, unseating of the sealsenables the bleeding of high pressure and the reseating of the seals.Therefore, by tuning closing force 210, electrochemical cell can beconfigured so that the seals are the first component to react to apressure increase instead of another component that's failure couldresult in release of hydrogen.

FIG. 6 shows a flow chart 600, for a method of tuning the seals ofelectrochemical cell 100. The method can include providingelectrochemical cell 100, which can have a plurality of seals in acascade seal configuration as described above. Next, the method caninclude applying an initial closing force to the electrochemical cellbased on the expected operating pressure. After applying an initialclosing force the cell can be energized and operation can begin. Duringoperation the pressure of the low, intermediate, and high pressure zoneswithin electrochemical cell 100 can be monitored continuously orintermittently. Based on the monitored pressures and the resultingopening force the closing force can be adjusted. Adjusting the closingforce can change the pressure at which at least one of the plurality ofseals unseats. This process can continue throughout the operation of theelectrochemical cell or can be configured to run for only a finiteperiod of time initially at startup. As required, operation ofelectrochemical cell can be ended.

It is contemplated that, in some embodiments, first seal 171 can unseatdue to the pressure of first fluid 172 in high pressure zone 170 withoutseparation of plates 150, 160. Similarly, it is contemplated that bothfirst seal 171 and second seal 181 can unseat due to the pressure offirst fluid 172 in high pressure zone 170 and second fluid 182 inintermediate pressure zone 182 without separation of plates 150, 160. Inthese embodiments, pressure of at least first fluid 172 and, in certainembodiments, both first fluid 172 and second fluid 182 can be monitored.Based on the monitored pressures, the closing force can be adjusted.Closing force 210 can be further tuned based on the geometry and/orthickness of first seal 171, second seal 181, and third seal 191relative to first shoulder 173, second groove 183, and third groove 193,respectively.

More or fewer seals and pressure zones are contemplated. For example, inanother embodiment as shown in FIG. 7, electrochemical cell 100 cancomprise a first seal 171 and second seal 181. Accordingly,electrochemical cell 100 as shown in FIG. 7 can comprise a first seal171 defining a high pressure zone 170. First seal 171 can be locatedbetween the bipolar plates 150, 160 and configured to contain a firstfluid 172 with high pressure zone 170. Electrochemical cell 100 canfurther comprise a second seal 181 defining an intermediate pressurezone 180. Second seal 182 can be located between bipolar plates 150, 160and configured to contain second fluid 182 within intermediate pressurezone 180. First seal 171 can be contained entirely with second seal 181.Electrochemical cell 100 can further comprise ancillary first seals 175,176. Ancillary seal 175 and 176 can be located outside first seal 171,but within second seal 181.

In addition, with regard to electrochemical cell 100, first fluid 172can be at a higher pressure than second fluid 182. First seal 171 andsecond seal 181 can have a generally rectangular cross-section. Thethickness of second seal 181 can be greater than first seal 171. Firstseal 171 can be configured to leak first fluid 172 into intermediatepressure zone 180 when first seal 171 unseats. In such an embodiment,electrochemical cell 100 can be configured to shutdown prior to theunseating of second seal 181 reducing the possibility of second fluid182 leaking from intermediate pressure zone 180.

First seal 171 and second seal 181 within electrochemical cell 100 canbe configured to remain seated preventing the leaking of first fluid 172and second fluid 182 when a closing force being applied to bipolarplates 150, 160 is greater than the opening force within bipolar plates150, 160. When closing force applied to bipolar plates 150, 160approaches the opening force within bipolar plates 150, 160, first seal171 can be configured to unseat before second seal 181 unseats causingfirst fluid 172 to leak past first seal 171 into intermediate pressurezone 180. First fluid 172 that leaks past first seal 171 can combinewith second fluid 182 and be recycled.

In another example (not shown), electrochemical cell 100 can comprisefirst seal 171, second seal 181, third seal 191, and a fourth seal. Inthis example, the fourth seal can be contained entirely within thirdseal 191, between second seal 181 and third seal 191. That is, thefourth seal can define a fourth pressure zone which can be, for example,a vacuum or hydrogen reclamation zone containing a fluid having apressure that is lower than the pressure of both second fluid 182 andthird fluid 192. The fourth seal can have a thickness that is greaterthan the thickness of second seal 181. In this manner, second seal 181can be configured to leak second fluid 182 into the fourth pressure zonewhen second seal 181 unseats.

FIGS. 8 and 11 illustrate exemplary embodiments of first seal 171. Asdiscussed above, first seal 171 defines high pressure zone 170, whichcan be configured to contain a first fluid 172 (e.g., hydrogen) withinhigh pressure zone 170. High pressure zone 170 can correspond to thehigh pressure cathode side 120 of PEM 130. Hydrogen formed at cathode120 can be collected in high pressure zone 170 and contained by firstseal 171. In some embodiments, hydrogen in high pressure zone 170 canhave a pressure greater than 15,000 psig.

As will be discussed in more detail below, first seal 171 can include anassembly of components capable of sealing a compartment ofelectrochemical cell 100, and withstanding pressures in excess of 15,000psig for long periods of time (e.g., greater than 10 years) andwithstand many pressure cycles (e.g., greater than 10,000 cycles). Inthe exemplary embodiments, the sealing components including a gasket300; a sealing surface 350 formed in one of bipolar plate 150, 160; andPEM 130. First seal 171 can be formed by compression of gasket 300against sealing surface 350, and compression of PEM 130 against gasket300. Other seals can include one or more features below and may be usedin conjunction with first seal 171. Additionally, it will be understoodthat the features described below can be used to seal other componentsof the electrochemical cell and/or can be used in cells that to notemploy the cascade seal configuration.

FIG. 8 is a cross-sectional view of electrochemical cell 100, accordingto an exemplary embodiment. As illustrated in FIG. 8, electrochemicalcell 100 includes an anode 110 compartment, a proton exchange membrane(PEM) 130, and a cathode compartment 120 disposed between bipolar plates150, 160. Sealing surface 350 can be formed in one of bipolar plates150, 160, and located adjacent a perimeter of the compartment to besealed. In FIG. 8, sealing surface 350 is located outside a perimeter ofcathode compartment 120. Gasket 300 is positioned between sealingsurface 350 and PEM 130.

During assembly of electrochemical cell 100, gasket 300 can becompressed against sealing surface 350 of bipolar plate 160 and PEM 130to form first seal 171, second seal 181, or third seal 191. Gasket 300can be configured such that, under compression by sealing surface 350,gasket 300 primarily undergoes plastic deformation. In particular,gasket 300 can be made from a “hard” material with a creep modulus andcompressive yield strength greater than the required sealing pressure,but lower than the compressive yield strength of sealing surface 350.For example, gasket 300 can be made from a material having a creepmodulus and/or compressive yield strength in a range sufficient towithstand pressure greater than 12,000 psi. Gasket 300 can have a yieldstrength higher than PEM 130, so that a seal is formed by compression ofthe soft PEM material against the surface of the hard gasket material.Alternately, gasket 300 can be made of a material having a compressiveyield strength less than the required sealing pressure. A compressivepressure greater than the required sealing pressure is still able to beapplied to gasket 300 due to the gasket being constrained by the wall ofbipolar plate 160 and the protrusions on sealing surface 350.

In some embodiments, gasket 300 can be made of a polymeric sealingmaterial including, but not limited to, Torlon®, polyether ether ketone(PEEK), polyethyleneimine (PEI), polycarbonate, polyimide, PET(polyethylene terephthalate), PEN (polyethylene naphthalate), HDPE(high-density polyethylene), polyurethane, acetal, nylon, polybutyleneterephthalate and polysulfone. The polymer gasket materials can be acidresistant and should not leach materials that are harmful to theoperation of electrochemical cell 100. In other embodiments, gasket 300can be made from metal material including, but not limited to, tin, tinalloys, stainless steel, silver, platinum, and gold. The metal gasketmaterials can be corrosion resistant or have a corrosion resistantcoating. In yet other embodiments, gasket 300 can be made of a compositeof polymeric and/or metallic materials.

The dimensions of gasket 300 including the shape, thickness, and widthof gasket 300 can vary, and can be based on the dimensions ofelectrochemical cell 100. In some embodiments, gasket 300 can have asubstantially rectilinear cross-section with a thickness in the range of0.25 inches to 0.001 inches. The thickness is measured along a verticalaxis (Y) of cell. In these embodiments, gasket 300 can have a width tothickness aspect ratio in the range of 3:1 to more than 25:1.

Sealing surface 350 can include one or more features configured to applysufficient pressure to plastically deform gasket 300 and create a seal.For example, sealing surface 350 can be a surface having one or moreprotrusions 360. In certain embodiments, compressive forces are appliedto create sufficient stresses that cause the gasket to plasticallydeform and create a sealing surface. The protrusions 360 can function asstress concentrators and when pressed into the seal, and can createlocalized stress in the material higher than a target sealing pressure.Although three protrusions 360 are depicted, it will be understood thata greater or lesser number of protrusions may be provided.

The protrusions can have any known geometry, sufficient to deform gasket300. For example, the protrusions can have a triangular configuration360 a (FIG. 9A), a cusp configuration 360 b (FIG. 9B), or a flat bladeconfiguration 360 c (FIG. 9C). Other contemplated geometries for theprotrusions include a partially rounded configuration, and asemicircular configuration. It is contemplated that the configuration ofeach protrusion can be different than the configuration of the otherprotrusions, or the same for all the protrusions. In FIGS. 9A-C theexemplary protrusions are shown having the same height, but any one ormore of could be configured to be taller or shorter than the rest. Forexample, every other protrusion may have the same height, the outer mostprotrusions may be taller and at the same height, the one or more innerprotrusions may be taller, the protrusions may descend or ascend inheight moving from left to right or right to left, or every protrusionmay be at a different height. Embodiments having protrusions ofdifferent heights may be configured to better account for variability inmachining tolerances of the other components.

Protrusions 360 and gasket 300 can be positioned relative to each otherto leave a small gap between protrusions 360 and a top surface of aportion of gasket 300. During assembly, protrusions 360 can becompressed against gasket 300 causing each protrusion 360 to press intoand seal with gasket 300. As further compressive forces are applied tobipolar plates 150, 160, sufficient stresses can be formed to causegasket 300 to plastically deform and create a seal.

In the exemplary embodiment, sealing surface can be a knife edge sealingsurface having one or more protrusions machined to a sharp knife edge.During assembly, these protrusions can be compressed against gasket 300causing the knife edge of each protrusion to press into and seal withgasket 300. As further compressive forces are applied to bipolar plates150, 160, sufficient stresses can be formed to cause gasket 300 toplastically deform and create a seal.

Gasket 300 can be compressed by a predetermined percentage of itsuncompressed thickness by selecting the appropriate height and widthdimensions for protrusions 360. In certain embodiments, protrusions 360can be arranged so as to deliberately create a non-uniform stress fieldwithin the gasket, where portions of the stress field are greater inmagnitude than the level of gas pressure being sealed.

FIGS. 9D and 9E provide a cross-section view of the sealing surface of abipolar plate depicted in FIG. 9A, in an uncompressed and compressedstate, respectively. In FIG. 9D, the width of gasket 300 is representedby W_(G1), the height of gasket 300 is represented by h_(G1), and thepocket depth in bipolar plate 160 is represented by d_(p). With respectto protrusions 360, the height is represented by h_(t), the spacingbetween the protrusions 360 is represented by S_(t).

In certain embodiments, the ratio of h_(G1):d_(p) can range from 0.8:1to 1.5:1, such as from 0.9:1 to 1.3:1, 0.9:1 to 1.4:1, from 1:1 to1.3:1, and from 1:1 to 1.2:1. In addition, the ratio of h_(t):h_(G1) canrange from 0.05:1 to 0.75:1, such as from 0.1:1 to 0.7:1, from 0.15:1 to0.65:1, from 0.2:1 to 0.6:1 and from 0.25:1 to 0.6:1. Further, the ratioof S_(t):h_(t) can range from 0.5:1 to 10:1 such as from 0.1:1 to 10:1,from 0.2:1 to 8:1, from 0.5:1 to 6:1, and from 1:1 to 5:1. In furtherembodiments, the ratio of h_(G1):d_(p), h_(t):h_(G1), and S_(t):h_(t)can all be within at least one range disclosed above.

In FIG. 9E, the width of gasket 300 is represented by W_(G2), the heightof gasket 300 is represented by h_(G2), and, in this embodiment in whichthe gasket is compressed, the pocket depth d_(p) in bipolar plate 160 isequal to h_(G2). In this embodiment, the pocket width is represented byW_(p).

In certain embodiments, the ratio of W_(G1):W_(p) ranges from 0.25:1 to2:1 such as from 0.5:1 to 2:1, from 0.75:1 to 2:1, from 1:1 to 2:1, andfrom 0.25:1 to 1:1. In addition, the ratio of W_(p):S_(t) can range from1:1 to 20:1, such as from 1:1 to 15:1, from 1:1 to 10:1, from 5:1 to20:1, and from 5:1 to 10:1. In further embodiments, the ratio ofW_(G1):W_(p) and W_(p):S_(t) can all be within at least one rangedisclosed above.

FIG. 9F illustrates a set of protrusions 360 having be a certain heighth_(t), spaced a certain distance S_(t) from one another, and the slopedsides of each protrusion can form an angle α. According to variousembodiments, the height of the protrusions 360 can range from 0.001 to0.020 inches, such as from 0.003 to 0.020 inches, from 0.005 to 0.015inches, and from 0.006 to 0.010 inches. According to variousembodiments, the distance between protrusions can range from 0.01 to 0.2inches, such as from 0.05 to 0.1 inches, from 0.02 to 0.05 inches, andfrom 0.02 to 0.03 inches. According to various embodiment, angle α canrange from 55 to 125 degrees, such as from 60 to 120 degrees, from 65 to115 degrees, from 75 to 105 degrees, and from 80 degrees to 100 degrees.In further embodiments, the height of the protrusions, distance betweenthe protrusions, and angle of the protrusions can all be within at leastone range disclosed above.

In alternative embodiments, sealing surface 350′ can be provided ongasket 300′ (FIG. 10) instead of one of the bipolar plates. According tothis embodiment, bipolar plate 160 can have a flat surface, and theportion of gasket 300′ in contact with bipolar plate 160 can havesealing surface 350′ including protrusions 360′. As in the embodimentdescribed above, protrusions 360′ can be machined to a sharp knife edge.Upon assembly of electrochemical cell 100, sealing surface 350′ can becompressed against bipolar plate 160 to plastically deform protrusions360′ of gasket 300′. As these protrusions plastically deform, the knifeedge of each protrusion can press into and seal with sealing surface350′.

Referring back to FIG. 8, PEM 130 can be compressed against a side ofgasket 300 that is opposite of sealing surface 350. In the exemplaryembodiment, PEM 130 can be formed of a material having a yield strengththat is lower (e.g., softer) than gasket 300. In this arrangement, aseal is formed by the compression of the soft PEM material against thesurface of the hard gasket material.

In alternative embodiments, a membrane or a membrane-like material canbe provided on at least one side of gasket 300. For example, a membraneor membrane-like material 370 can be provided between bipolar plate 160and gasket 300 (FIG. 11). In some embodiments, membrane 370 can also beprovided between gasket 300 and PEM 130 (e.g., on both sides of gasket300).

Membrane 370 can be a “soft gasket,” used in place of the knife-edgeseal. In particular, membrane 370 can be formed of a “soft” materialhaving a creep modulus and compressive yield strength that is lower thangasket 300. A seal can be formed by compression of membrane 370 againstgasket 300 and bipolar plate 160. Where a membrane 370 is provided onboth sides of gasket 300, a seal can also be formed by compression ofmembrane 370 against gasket 300 and PEM 130.

In some embodiments, membrane 370 can be bonded to gasket 300 byadhesive materials or other known bonding methods. Such methods includehot-pressing or ultrasonic welding. Bonding of membrane 370 to gasket300 can aid in assembly of electrochemical cell 100, and can improve theseal between membrane 370 and gasket 300.

In some embodiments, the perimeter of anode compartment 110 can extendbeyond the perimeter of the sealed cathode compartment 120 (FIGS.12A-12D). In those embodiments, a thin gas diffusion layer 380 can beprovided between PEM 130 and the portion of anode compartment 110 thatextends beyond the perimeter of cathode compartment 120. In theexemplary embodiment shown in FIGS. 12A-12D, gas diffusion layer 380 isdisposed along a side of PEM 130 that is opposite to gasket 300.

Gas diffusion layer 380 can serve as diffusion media enabling thetransport of gases and liquids within the cell, can aid in the removalof heat and process water from the cell, and in some cases, can providesome mechanical support to PEM 130. Gas diffusion layer 380 can comprisea woven or non-woven carbon or other conductive material cloth. Incertain embodiments, “frit”-type densely sintered metals, screen packs,expanded metals, metal foam, or three-dimensional porous metallicsubstrates can be used in combination with or as a replacement for atleast a portion of gas diffusion layer 380 to provide structuralsupport.

Also included in these embodiments is a reinforcement layer 385, whichcan have any size, shape, and/or configuration sufficient to providesupport to PEM 130. Reinforcement layer 385 can be configured to preventextrusion or tearing of PEM 130 due to excessive stress caused by thenon-uniform flow fields. In certain embodiments, reinforcement layer 385is formed from a polyester resin.

In the exemplary embodiment shown in FIGS. 12A and 12C, reinforcementlayer 385 has a length dimension that is substantially the same asgasket 300. In other exemplary embodiments shown in FIGS. 12B and 12D,reinforcement layer 385 has a length that is greater than a length ofgasket 300, e.g., a portion of reinforcement layer 385 extends beyond anedge of gasket 300. In the embodiments shown in FIGS. 12B and 12D,reinforcement layer 385 provides support to PEM 130 in the event PEM 130bends at the edge of gasket 300.

In various embodiments, the sealing engagement between gasket 300,sealing surface 350, and PEM 130, can be tested ex-situ before assemblyof electrochemical cell 100 without loss of integrity of the seal. Inparticular, a shim 390 can be placed between bipolar plates 150, 160 toprevent full compression of gasket 300 during ex-situ testing. This canensure that gasket 300 experiences a high stress at sealing surface 350when fully compressed in the stack. In the exemplary embodiment shown inFIG. 13, shim 390 is shown between bipolar plates 150, 160 to increasethe depth of seal 171 and prevent full deformation of the gasket 300during ex-situ testing.

The seal assembly described above can provide several advantages. Whileconventional elastomeric seals require less compressive force, theelastomeric seals are susceptible to extrusion and explosivedecompression. The disclosed gasket 300, in contrast, can be moreresilient. As noted above, the disclosed gasket 300 can be selected tobe softer than sealing surface 350 and harder than PEM 130. Accordingly,gasket 300 can be capable of sealing pressures in excess of 15,000 psi.Additionally, gasket 300 can provide a greater dimensional tolerance inthe flow field thicknesses and pocket depths than conventional sealingdesigns. As gasket 300 can deform over a relatively large range ofthicknesses, gasket 300 can accommodate variations in pocket depths andflow fields while still maintaining relatively uniform compressionpressure.

FIG. 14 shows one embodiment of bipolar plates 150 and 160 comprising atwo-piece bipolar plate 800 comprising a first component 801 and asecond component 802 configured for a cascade seal configuration. Firstcomponent 801 can form a void 803 in fluid communication with a flowstructure 805.

Electrochemical cell 100, as shown in FIG. 1, can further compriseelectrically-conductive gas diffusion layers within electrochemical cell100 on each side of MEA 140. Gas diffusion layers can serve as diffusionmedia enabling the transport of gases and liquids within the cell,provide electrical conduction between bipolar plates 150 and 160 and PEM130, aid in the removal of heat and process water from the cell, and insome cases, provide mechanical support to PEM 140. In addition, channels(not shown), known as flow fields, in bipolar plates 150 and 160 can beconfigured to supply gases to anode 110 and cathode 120 of MEA 140.Reactant gases on each side of PEM 130 can flow through flow fields anddiffuse through the porous gas diffusion layers. The flow fields and thegas diffusion layers can be positioned contiguously and coupled by theinternal fluid streams. Accordingly, the flow field and the gasdiffusion layers can collectively form flow structure 805.

First component 801 and second component 802 can be generally flat andhave a generally rectangular profile. In other embodiments, components801 and 802 can have a profile shaped like a square, a “race-track”(i.e., a substantially rectangular shape with semi-elliptical latersides), circle, oval, elliptical, or other shape. The shape of firstcomponent 801 and second component 802 can correspond to the othercomponents of electrochemical cell 100 (e.g., cathode, anode, PEM, flowstructure, etc.) or electrochemical cell stack.

First component 801 and second component 802 can each be formed of oneor more materials. First component 801 and second component 802 can beformed of the same materials or different materials. Component 801 and802 can be formed of a metal, such as, stainless steel, titanium,aluminum, nickel, iron, etc., or a metal alloy, such as, nickel chromealloy, nickel-tin alloy, or a combination thereof.

First component 801 and second component 802 can comprise a cladmaterial, for example, aluminum clad with stainless steel on one or moreregions. Cladding can provide the advantages of both metals, forexample, in the case of a bipolar plate fabricated from stainlesssteel-clad aluminum, the stainless steel protects the aluminum core fromcorrosion during cell operation, while providing the superior materialproperties of aluminum, such as, high strength-to-weight ratio, highthermal and electrical conductivity, etc. In other embodiments, firstcomponent 801 can comprise anodized, sealed, and primed aluminum. Othercoatings such as paint or powder coat could be used with component 801.

In some embodiments, first component 801 can be formed of a composite,such as, carbon fiber, graphite, glass-reinforced polymer, thermoplasticcomposites. In some embodiments, first component 801 can be formed of ametal which is coated to prevent both corrosion and electricalconduction.

According to various embodiments, first component 801 can be generallynon-conductive reducing the likelihood of shorting between theelectrochemical cells. Second component 802 can be formed of one or morematerials that provide electrical conductivity as well as corrosionresistance during cell operation. For example, second component 802 canbe configured to be electrically conductive in the region where theactive cell components sit (e.g., flow structure, MEA, etc.).

First component 801 and second component 802 can be configured forcoplanar coupling. First component 801 and second component 802 can bereleasably coupled or fixedly coupled. One or more attachment mechanismscan be used including, for example, bonding material, welding, brazing,soldering, diffusion bonding, ultrasonic welding, laser welding,stamping, riveting, resistance welding, or sintering. In someembodiments, the bonding material may include an adhesive. Suitableadhesives include, for example, glues, epoxies, cyanoacrylates,thermoplastic sheets (including heat bonded thermoplastic sheets)urethanes, anaerobic, UV-cure, and other polymers. In some embodiments,first component 801 and second component 802 can be coupled by afriction fit. For example, one or more seals between the components canproduce adequate frictional force between the components when compressedto prevent unintended sliding.

In other embodiments, first component 801 and second component 802 canbe releasably coupled using fasteners, for example, screws, bolts,clips, or other similar mechanisms. In other embodiments, compressionrods and nuts or other, similar mechanical compression system can passthrough bipolar plate 800 or along the outside and be used to compressfirst component 801 and second component 802 together as electrochemicalcell 100 or a plurality of electrochemical cells 100 are compressed in astack.

Coupled first component 801 and second component 802 can form aplurality of different pressure zones and a plurality of seals candefine one or more different pressure zones. FIG. 14 shows the pluralityof different seals and pressure zones. As shown in FIG. 14, theplurality of seals can include a first seal 871, a second seal 881, anda third seal 891. First seal 871 can be contained entirely within secondseal 881 and second seal 881 can be contained entirely within third seal891. The shape of first seal 871, second seal 881, and third seal 891can generally correspond to the shape of bipolar plate 800, as shown inFIG. 14.

In certain embodiments, first seal 871 is formed from protrusions 360 asdescribed above. For example, the protrusions can have a triangularconfiguration 360 a (FIG. 9A), a cusp configuration 360 b (FIG. 9B), aflat blade configuration 360 c (FIG. 9C), or any other geometrysufficient to form a seal surface. In other embodiments, at least two offirst seal 871, second seal 881, and third seal 891 are formed fromprotrusions 360, and in certain embodiments, all three of first seal871, second seal 881, and third seal 891 are formed from protrusions360.

First seal 871 can define a portion of high pressure zone 870 and beconfigured to contain a first fluid 872 (e.g., hydrogen) within highpressure zone 870. First seal 871 can delimit the outer boundaries ofhigh pressure zone 870 at least between components 801 and 802. Highpressure zone 870 can include flow structure 805 extending through void803 when first component 801 and second component 802 are coupled. Firstfluid 872 can flow throughout high pressure zone 870 thorough flowstructure 805 from cathode 130.

Hydrogen formed at cathode 130 can be collected in high pressure zone870 and the connection between first component 801 and second component802 can be sealed by first seal 871. Hydrogen within high pressure zone870 can be compressed and, as a result, increase in pressure as more andmore hydrogen is formed in high pressure zone 870. Hydrogen in highpressure zone 870 can be compressed to a pressure greater than 15,000psi. Pressure within high pressure zone 870 can apply a separation forceon first component 801 and second components 802.

As shown in FIG. 14, first seal 871 can be configured to extend aroundthe exterior of common passages 804. Common passages 804 can beconfigured to supply or discharge first fluid 872 from high pressurezone 870. Common passages 804 can be in fluid communication with commonpassages of adjacent electrochemical cells in a multi-cellelectrochemical compressor.

Second seal 881 can define the outer circumference of intermediatepressure zone 880. Intermediate pressure zone 880 can comprise anintermediate pressure volume 883 delimited by first seal 871, secondseal 881, first component 801 and second component 802. Intermediatepressure zone 880 can be configured to contain a second fluid 882.Intermediate pressure zone 880 can further comprise one or moreintermediate pressure ports 884.

Intermediate pressure volume 883 can be configured to collect and directsecond fluid 882 to intermediate pressure ports 884. As shown in FIG.14, intermediate pressure volume 883 can extend around the circumferenceof high pressure zone 870 separated by first seal 871. Thecross-sectional area and volume of intermediate pressure volume 883 canvary based on the geometry of first component 801, second component 802,first seal 871, and second seal 881.

In other embodiments, intermediate pressure volume 883 can be separatedinto a plurality of intermediate pressure volumes 883, for example, 2,3, 4 or more intermediate pressure volumes 883. The plurality ofintermediate pressure volumes 883 can be separated by a plurality ofseals. As shown in FIG. 14, intermediate pressure volume 883 can beseparated into two intermediate pressure volumes 883. For example, asshown in FIG. 14, first seal 871 can extend across intermediate pressurevolume 883 to second seal 881. The portions of first seal 881 thatextend around common passages 804 can connect with second seal 882separating intermediate pressure volume 883 into two intermediatepressure volumes 883.

As shown in FIG. 14, the one or more intermediate pressure volumes 883can each be in fluid communication with one or more intermediatepressure ports 884. Intermediate pressure ports 884 can be configured todischarge second fluid 882 contained within intermediate pressurevolumes 883. The shape of intermediate pressure ports 884 can vary. Forexample, intermediate pressure ports 884 can be square, rectangle,triangle, polygon, circle, oval, or other shape. The number ofintermediate pressure ports 884 per intermediate pressure volume 883 canvary from 1 to about 25 or more. The cross-sectional area ofintermediate pressure ports 884 can vary. For example, the diameter ofcircular intermediate pressure ports 884 can range from less than about0.1 inch to about 1 inch or more. As shown in FIG. 14, intermediatepressure ports 884 can be evenly spaced between first seal 871 andsecond seal 881 and evenly distributed along the length of bipolar plate800. Alternately, intermediate pressure ports 884 can be non-evenlyspaced between first seal 871 and second seal 881 and/or have variablespacing along the length of bipolar plate 800. In other embodiments,intermediate pressure ports 884 can extend the full circumference ofintermediate pressure zone 880.

Second fluid 882 discharged via intermediate pressure ports 884 can beresupplied to electrochemical cell 100. For example, second fluid 882can return to intermediate pressure zone 180. In other embodiments,second fluid 882 discharged via intermediate pressure ports 884 can becollected and recycled. Second fluid 882 in intermediate pressure zone880 can generally be lower pressure than first fluid 872 in highpressure zone 870.

Third seal 891 can define low pressure zone 890 and be configured tocontain a third fluid 892 within low pressure zone 890. Low pressurezone 890 can comprise a low pressure volume 893 delimited by second seal881, third seal 891, first component 801, and second component 802. Lowpressure zone 890 can be configured to contain a third fluid 892. Lowpressure zone 890 can further comprise one or more low pressure ports894.

Low pressure volume 893 can be configured to collect and direct thirdfluid 892 to low pressure ports 894. As shown in FIG. 14, low pressurevolume 893 can extend around the circumference of intermediate pressurezone 880 separated by second seal 881. The cross-sectional area andvolume of low pressure volume 893 can vary based on the geometry offirst component 801, second component 802, second seal 881, and thirdseal 891. According to various embodiments, the intermediate pressurevolume 883 can be greater than or less than the volume of low pressurevolume 893.

As shown in FIG. 14, the one or more low pressure volumes 893 can eachbe in fluid communication with one or more low pressure ports 894. Lowpressure ports 894 can be configured to discharge third fluid 892contained within low pressure volumes 893. The shape of low pressureports 894 can vary. For example, low pressure ports 894 can be square,rectangle, triangle, polygon, circle, oval, or other shape. The numberof low pressure ports 894 per low pressure volume 893 can vary from 1 to50 or more. The cross-sectional area of low pressure ports 894 can vary.For example, the diameter of circular low pressure ports 894 can rangefrom less than 0.1 inch to 1 inch or more. As shown in FIG. 14, lowpressure ports 894 can be spaced between second seal 881 and third seal891 and evenly staggered along the length of bipolar plate 800. In otherembodiments, low pressure ports 894 can extend the full circumference oflow pressure zone 890.

Third fluid 892 discharged via low pressure ports 894 can be resuppliedto electrochemical cell 100. For example, third fluid 892 can return tolow pressure zone 190. In other embodiments, third fluid 892 dischargedvia intermediate pressure ports 894 can be collected and recycled. Thirdfluid 892 in low pressure zone 890 can generally be lower pressure thanfirst fluid 872 in high pressure zone 870 and second fluid 882 inintermediate pressure zone 880.

The cascade seal configuration between first component 801 and secondcomponent 802 as described above can be implemented in bipolar plate 150and 160 of electrochemical cell 100, as described above. In otherembodiments, the cascade seal configuration between components 801 and802 can be implemented in other electrochemical cells in which a cascadeseal configuration is not utilized between the two bipolar plates.Therefore, both cascade seal configurations as described above can beindependent of one another such that either one can be utilizedindividually in an electrochemical cell or they can be utilized inconjunction in the same electrochemical cell.

In some embodiments, first component 801 and second component 802 caninclude interlocking features. The interlocking features may form amating geometry sufficient to secure first component 801 and secondcomponent 802 together. For example, first component 801 may compriseone or more protrusions, and second component 802 may comprise one ormore indentations. However, it is further contemplated first component801 and second component 802 may comprise various attachment mechanisms.Interlocking features may comprise various shapes and sizes. Forexample, protrusions and indentations may be formed cylindrical, round,elliptical, rectangular, or square in shape. Additionally, protrusionsand indentations may include various polygonal shapes.

As shown in FIG. 14, interlocking features may include variousconnections configured to seal first component 801 and second component802. For example, interlocking features may include first seal 871,second seal 881, and third seal 891 and the corresponding seal cavity inwhich they can rest. First component 801 and second component 802 caninclude a plurality of seal cavities configured to receive at least aportion of first seal 871, second seal 881, and third seal 891. Eachseal cavity can comprise an extrusion into first component 801, secondcomponent 802 or both components 801 and 802. The extrusion dimensionsand geometry can correspond to the dimensions and cross-sectionalgeometry of first seal 871, second seal 881, and third seal 891.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present disclosure herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the present disclosure being indicated by the followingclaims.

What is claimed is:
 1. An electrochemical cell, comprising: a pair ofbipolar plates and a membrane electrode assembly located between thepair of bipolar plates, wherein the membrane electrode assemblycomprises an anode compartment, a cathode compartment, and a protonexchange membrane disposed there between; a sealing surface formed ononly one of the pair of bipolar plates, wherein the sealing surfaceincludes a plurality of protrusions; and a gasket located between thesealing surface and a single surface of the proton exchange membrane,wherein: a first side of the proton exchange membrane is in contact witha first bipolar plate, the gasket and the sealing surface create a sealabout only one of the cathode compartment or the anode compartment, andthe gasket has a yield strength greater than a yield strength of theproton exchange membrane material.
 2. The electrochemical cell of claim1, wherein the sealing surface comprises a material that has a yieldstrength greater than a yield strength of the gasket.
 3. Theelectrochemical cell of claim 1, wherein a reinforcement layer isdisposed along a side of the proton exchange membrane that is oppositeto the side along which the gasket is disposed.
 4. The electrochemicalcell of claim 3, wherein the reinforcement layer is located in the anodecompartment.
 5. The electrochemical cell of claim 4, wherein thereinforcement layer has a length dimension that is greater than thelength dimension of the gasket.
 6. The electrochemical cell of claim 1,wherein the gasket, in its uncompressed state, has a ratio between aheight of the gasket (h_(G1)) and a pocket depth (d_(p)) in the bipolarplate ranging from 0.8:1 to 1.5:1.
 7. The electrochemical cell of claim1, wherein the gasket, in its uncompressed state, has a ratio between aheight of the protrusions (h_(t)) and a height of the gasket (h_(G1))ranging from 0.05:1 to 0.75:1.
 8. The electrochemical cell of claim 1,wherein the gasket, in its uncompressed state, has a ratio between aspacing of the protrusions (S_(t)) and a height of the protrusions(h_(t)) ranging from 0.5:1 to 10:1.
 9. The electrochemical cell of claim1, wherein the gasket, in its uncompressed state, has a ratio between aheight of the gasket (h_(G1)) and a pocket depth (d_(p)) in the bipolarplate ranging from 0.8:1 to 1.5:1, a ratio between a height of theprotrusions (h_(t)) and the height of the gasket (h_(G1)) ranging from0.05:1 to 0.75:1, and a ratio between a spacing between the protrusions(S_(t)) and the height of the protrusions (h_(t)) ranging from 0.5:1 to10:1.
 10. The electrochemical cell of claim 1, wherein the protrusionshave a height ranging from 0.001 to 0.02 inches, a distance betweenprotrusions ranging from 0.01 to 0.2 inches, and a protrusion angleranging from 55 to 125 degrees.
 11. The electrochemical cell of claim 1,wherein the bipolar plates directly contact each other and the protonexchange membrane.
 12. The electrochemical cell of claim 1, wherein asecond side of the proton exchange membrane is in contact with a secondbipolar plate.